1. Field of the Invention
The present invention relates to a fuel supply apparatus for supplying high pressure fuel to a fuel injection device of an internal combustion engine.
2. Description of Related Art
One type of known fuel supply apparatus, such as disclosed in Japanese Unexamined Patent Publication No. JP-A-8-14140, has an electromagnetic valve installed in a fuel intake side of a fuel pressurizing chamber. According to the fuel supply apparatus, fuel is sucked into the fuel pressurizing chamber by lowering a plunger when the electromagnetic valve is opened, and the fuel is pressurized by elevating the plunger when the electromagnetic valve is closed. Thus, as shown in FIG. 15, a housing 101 of a high pressure fuel pump 100 is generally coupled with a fuel inlet 110, a delivery valve 111, and a pressure regulator 112 by a threadable attachment radially toward a center of an axis of a plunger 102.
However, according to the structure in which the respective parts are threadably attached to the housing 101 radially toward the center of the axis of the plunger 102, axial forces caused by such threadable attachment are applied to seat surfaces of the housing 101 where the respective attachment parts are fixedly engaged, and accordingly, the axial forces are applied to a cylinder 103. Then, as shown in FIG. 16, the inner peripheral surface of the cylinder 103 having a circular shape shown by a two-dotted chain line 120 before the threadable attachment, is deformed into a shape shown by a bold line 121 after the threadable attachment. That is, a clearance "h" between the plunger 102 and the cylinder 103 which has been uniform in a circumferential direction before the threadable attachment is changed to (h-.sigma.) at portions where the clearance is reduced after the threadable attachment.
When the clearance is partially reduced in this way, as a result of preventing fuel as a lubricant from being sufficiently supplied to the portions where the clearance is reduced, seizing may be caused at sliding portions between the plunger 102 and the cylinder 103, and a reciprocating motion of the plunger 102 may be prevented.
Furthermore, the attachment parts are attached radially to the housing 101, and positions of seat surfaces of the housing 101 for fixedly engaging the respective attachment parts cannot be disposed excessively proximate to the cylinder 103 to prevent deformation of the cylinder 103.
Accordingly, a volume of the housing interposed among the attachment parts is increased, and the housing cannot be reduced in size. Further, since fuel passages for being connected to the respective attachment parts need to be formed respectively, the number of manufacturing process for the fuel passages cannot be reduced.
Furthermore, according to the high pressure fuel pump disclosed in JP-A-8-14140, as shown FIG. 17, when a plunger 102 is lowered in the lower direction in FIG. 17 in accordance with the opening of an electromagnetic valve 210, low pressure fuel is sucked from a fuel intake passage 202 into a fuel pressurizing chamber 204 via a fuel introducing chamber 203, and an opening portion of an electromagnetic valve 210 between a valve member 211 and a valve seat 212.
However, when the number of crests of a cam for reciprocating the plunger 102 is increased and a reciprocating speed of the plunger 102 is increased in order to increase a fuel delivery amount of the high pressure fuel pump 100 per predetermined time period, a fuel intake time period per intake stroke is shortened. The high pressure fuel pump 100 has only one intake path for sucking fuel from the opening portion between the valve member 211 and the valve seat 212 to the fuel pressurizing chamber 204 when the electromagnetic valve 210 is opened. Therefore, a fuel intake failure may result the fuel intake time period is shortened and a necessary fuel amount is not be sucked. It is conceivable to increase a lift amount of the valve member of the electromagnetic valve or to increase an opening area by increasing a seat diameter of the valve member of the electromagnetic valve in order to avoid an intake failure. However, the structure of the conventional electromagnetic valve would need to be changed in a large scale. As a result, there may be an increase in a manufacturing cost because the electromagnetic valve is increased in size. Further, the response of the electromagnetic valve will be lessened in proportion to an increase in size of the electromagnetic valve.
In order to avoid the fuel intake failure accompanied by shortened fuel intake time period, a high pressure fuel pump 220 as shown in FIG. 18 may be provided. In the case where the plunger 102 is lowered when the electromagnetic valve 210 is opened, low pressure fuel is sucked into the fuel pressurizing chamber 204 from a fuel intake passage 221 via the fuel introducing chamber 203 and the opening portion between the valve member 211 and the valve seat 212. Furthermore, when the plunger 102 is lowered to a position shown in FIG. 18, low pressure fuel is sucked into the fuel pressurizing chamber 204 directly from a fuel intake passage 222. Therefore, it has two intake paths for fuel intake and accordingly, it is intended to prevent a reduction in the fuel intake amount per intake stroke, and to increase the fuel delivery amount per predetermined time period even if the fuel intake time period is shortened.
However, a pressurized transferring of fuel is not started unless an outer wall of the plunger 102 closes the fuel intake passage 222 in accordance with the elevation of the plunger 102. Further, since the fuel intake passage 222 is closed by the outer wall of the plunger 102 in the pressurized transferring stroke, fuel cannot be sufficiently pressurized unless the plunger 102 is further elevated to ensure a sufficient seal length for the fuel intake passage 222 after closing the fuel intake passage 222 by the plunger 102. Accordingly, a fuel delivery amount in respect of a volume of the fuel pressurizing chamber 204 when the plunger 102 reaches the bottom dead point, that is, the fuel delivery efficiency, may be lessened.